In the manufacture of photographic films and papers, a support is commonly coated with multiple layers. The different layers have different individual functions in the final product, and in many instances it is necessary that the layers remain distinct and not mix with one another. For example, a simple color photographic film can have a subcoating, a blue-sensitive layer, a green-sensitive layer, a red-sensitive layer, one or more color filtering coatings, etc. Films with about 15 layers have been described, e.g. in EP 257,515, incorporated by reference herein.
In forming photographic elements, the layers can be applied to the support by various procedures known in the art. For example, the layers can be applied by dip coating, roller coating, spray coating, bead coating, and the like.
Two or more layers can be simultaneously applied as illustrated by U.S. Pat. Nos. 2,761,791, 3,508,847, 3,539,644, and such other patents cited in Research Disclosure No. 308, December 1989, pp. 1007-8, incorporated by reference herein. There, coating and drying procedures are discussed.
High purity gelatins are required for (imaging/photographic) applications. One gelatin property of interest is absorbance at 420 nm (A420), commonly know as color. The lower the A420 of gelatin the clearer the gelatin layer is in coated products. The A420 of gelatin is one of the defining factors for determining applicability of the gelatin for imaging applications. Edible gelatins are typically higher than photographic gelatins in A420. Two other gelatin properties critical to imaging applications are viscosity and Gel or Bloom strength. High Gel strength is required for gelatin setting properties. Typical alkaline processed bone gelatins contain high Gel strength and high viscosity. Viscosity is typically controlled during the gelatin manufacturing process with heat treatment. Heat treatment reduces both Gel strength and viscosity. Ideally, a gelatin with high Gel strength and low viscosity would be advantageous to coated products, in that coating speeds could be increased with no loss in gelatin setting properties. The gelatin described in this invention is optimized for each of the properties described above. This novel gelatin combines very low color and high Gel strength within a wide range of viscosities. Typically, photographic gelatin requires a Gel strength of greater than 200 and a viscosity of from 7 to 9 cp.